Electrostatic method and apparatus for atomizing and for coating



Oct. 8, 1957 M. R. MILLER ELECTROSTATIC METHOD AND APPARATUS FORATOMIZING AND FOR COATING 2 Sheets-Sheet 1 Filed July 14, 1953 INVENTORTM r0/ v HI MIL LEI? ATTORNEY Oct. 8, 1957 M. R. MILLER ELECTROSTATICMETHOD AND APPARATUS FOR ATOMIZING AND FOR COATING 2 Sheets-Sheet 2Filed July 14, 1955 JNVENTOR.

ME/PTO/V R. M/LLER BY A A7- 5 A zro R/VE) United States PatentELECTROSTATIC METHOD AND APPARATUS FOR ATOMIZING AND FOR COATING MertonR. Miller, Whittier, Calif., assignor to Ransburg Electra-Coating Corp.,Indianapolis, Ind., a corporation of Indiana Application July 14, 1953,Serial No. 367,880

19 Claims. (Cl. 11793) This invention relates generally to improvementsin methods and apparatus for atomizing liquids and especially to methodsand apparatus in which the liquid atomized is a coating material and inwhich the atomized material is electrostatically deposited on articlesto be coated.

One object of the present invention is to provide a method and apparatusfor atomizing liquids in which novel control is achieved over liquidsupplied to a site of atomization.

Another object of the present invention is to provide a method andapparatus for atomizing liquids in which the direction of the spray iscontrollable and adjustable.

Still another object of the present invention is to provide novelapparatus for atomizing liquids which may be operated intermittentlyand, if desired, in co-ordination with the movement past it of articlesto be coated with the atomized liquid.

A further object of the present invention is to make possible theelectrostatic atomization of a liquid fed to a site of atomization as afilm on the surface of a roller of such large diameter that without adischarge member it is impracticable to maintain at the surface of theroller an electrostatic field of suflicient strength to produceatomization.

In practicing the invention, the liquid material to be atomized is movedto a site of atomization in the form of a film, preferably on thesurface of a rotating member between which and the article or articlesto be coated an electrostatic field is maintained. To concentrate thefield, or increase its potential gradient, where necessary or desired atthe site of atomization a discharge member may be placed in the path ofthe moving film to deform it and increase its curvature. Anelectrostatic field is created between the site of atomization and anarticle or articles 7 to be coated, and the atomized particles proceedunder the influence of such field as a divergent spray for electrostaticdeposition on such article or articles. If it is desired to produce aconfining effect on the atomizing spray, a feed member having amaterally larger surface area than the surface area of the dischargemember should be used. It it is desired to make the direction of theatomized spray adjustable, the discharge member is mounted for movementconcentrically relative to the feed member so it may assume differentrelative positions with respect to the film-supporting surface of thefeed member. Means may be provided for stopping atomization which movesthe discharge member out of the path of movement of the liquid filmsupported on the feed member; and if desired, such discharge-membermovement may be automatically coordinated with movement of the articlesbeing coated.

The rotating feed member on whose surface the film is carried to thesite of atomization may be provided with a shield or shroud whichpartially surrounds the feed member, such shield being interrupted toprovide an opening for emergence of the spray. Such a shroud retardsevaporation of the liquid in the film and aids in the appended claims.

2,809,128 Patented Oct. 8, i957 ice collection for reuse of any liquidwhich leaves the rotating member otherwise than in the spray projectedtoward the article.

For a better understanding of the invention, together with other andfurther objects, reference ishad to the following description taken inconnection with the following drawings, and its scope will be pointedout in the In the accompanying drawings:

Fig. 1 is an isometric view illustrating the invention as embodied inapparatus for electrostatically atomizing a liquid coating material andelectrostatically depositing the atomized particles on a moving sheet;

Fig. 2 is a partial isometric view of modified electrostatic atomizingapparatus;

Fig. 3 is a diagrammatic elevational view of another modification ofelectrostatic atomizing apparatus utilized for coating sheet material;

Fig. 4 is an end view partially in section of still another modifiedelectrostatic atomizing apparatus for coating articles; and

Fig. 5 is a section through Fig. 4 along the line 55 looking in thedirection of the arrows.

Referring to the drawings and more particularly to Fig. 1, a sheet 10 ismoved in the direction of the arrow 12 by suitable means (not shown)past and in spaced relation to an atomizing device 14. As the sheet 16moves past the atomizer 14 a spray of electrostatically atomized liquidfrom the atomizer 14 is deposited on the sheet.

The electrostatic atomization and deposition of the liquid coatingmaterial is effected by an electrostatic field of appropriatecharacteristics which is established between the atomizer 14 and thesheet 10. For this purpose the sheet 10 may be grounded in any suitablemanner and the atomizer 14 insulated from ground and connected by meansof conductor 16 to the ungrounded terminal of a high-voltage source 18,the other terminal of which is grounded.

The atomizer 14 comprises a supporting structure which includes verticalposts 20, 21, 22 and 23 of electrical insulating material and horizontalframe 24. A dip tank 26 is suitably mounted on the frame 24. A roller28, provided with liquid supporting surface 29 and shaft 30, is

rotatably mounted on bearings 32, which are suitably afiixed to theframe 24. The roller 28 is mounted relative to the tank 26 to dip intoliquid in the tank as it is rotated about its axis so that a thin filmof liquid is applied from the tank onto the surface 29. It is desirablethat this film be thin enough so that negligible running and saggingoccur on the roller 28. Factors which govern the thickness of the filmthat is produced are the rate of rotation of the roller 28 and thedensity, viscosity and surface tension of the liquid. As an aid toobtaining the desired thickness of liquid film on the surface 29, adoctor blade 34 may be provided. In Fig. 1 this blade is shown asmounted on the tank 26 for ad justment relative to the surface 29 bymeans of screws 36 and 38.

The roller 28 may be provided with a cover 40 mounted on bracket 42 madeof insulating material which is supported on the vertical posts 22 and23 for reducing to a minimum evaporation from the liquid filmdistributed over the surface 29.

The motive power for rotating the roller 28 is provided by motor 44through variable speed transmissions 46 and 48, gears 50 and 52, shaft54 and belt 56 made of insulating material.

The liquid coating material in the tank 26 which is applied to theroller 28 is supplied from container 58 through pipes 60 and 62 ofinsulating material by means of pump 64, which may be of any suitabletype available commercially. The pump 64 is driven by motor 44 throughvariable transmissions 46 and 66 and gears 68 and 70. The tank 26 isprovided with an overflow pipe 72 made of insulating material whichleads to the container 58 and serves to maintain a constant level ofliquid in the tank 26 by returning to container 58 liquid in tank 26which reaches a predetermined level.

A discharge member 74, which is shown in Fig. l as a wire, is supportedin spaced relation to the sheet and adjacent the peripheral surface 29of the roller 28 by means of support members 76 and 78 of insulatingmaterial which are movable to carry the discharge member into and out ofcontact with the liquid film on the roller. Conveniently, the members 76and 78 are slidahly associated respectively with solenoids 80 and 82.are biased by appropriate yielding means (not shown) to move thedischarge member 74 out of contact with the liquid film on the surface29, and are movable upon energization of the solenoids 80 and 82 tocarry the discharge member in the opposite direction into engagementwith the liquid film on the roller. The discharge member 74 is connectedto the ungrounded terminal of the high-voltage source 18 by conductor 16for establishing a hi h gradient electrostatic field adjacent thereto.When the discharge member is in contact with the liquid film on therotating roller 28 such film is deformed by the discharge member andtransferred thereto. The electrostatic field adiacent the dischargemember 74 shapes the deformed liouid into a series of cusps 75 from thetips of which the liquid is electrostatically atomized andelectrostatically deposited on sheet 10. Positioning the roller or feedmember immediately adiacent the discharge member results in shielding aportion of the surface of the discharge member and limits atomization toonly the unshielded surface of the discharge member. Thus, it has aconfining effect on the spray produced. This shielding effect may bevaried by changing the size of the feed member, the discharge member orboth.

Electrostatic atomization by the device just described may beinterrupted or stopped by dc-energizing the highvoltage source 18 or bymoving the discharge member 74 out of contact with the liquid film. Thelatter operation may be accomplished by de-energizing the solenoiddevices 80 and 82.

As shown the solenoids 80 and 82 are connected in parallel by conductors84 and 86 and are connected to a suitable source of current byconductors 87, 88 and 89. A switch 90 is connected between conductors 88and 89. This switch is provided with a. spring biased lever 91 which islocated in the path of movement of the sheet 10 and which normallymaintains the switch 90 open and the solenoids 80 and 82 de-energized.Under this condition the discharge member 74 is held out of contact withthe liquid film on the surface 29. However,

when the lever 91 is moved by the sheet 10 the switch 90 is closed andthe solenoids 80 and 82 are energized to move the discharge member 74into contact with the liquid film on the surface 29.

The variable speed transmissions 46, 48 and 66 are arranged andconstructed so that the ratio of fluid delivery of the pump 64 to therate of rotation of the roller 28 may be established by the properadjustment of knobs 92 and 94 of variable speed transmissions 48 and 66respectively. For normal operation the speed of the pump and the rate ofrotation of the roller are adjusted by the knobs 92 and 94 so that theliquid delivery of the pump to the tank 26 is slightly in excess of thevolume of liquid delivered by the rotating roller from the tank 26 tothe discharge member. After the knobs 92 and 94 are set to conform tothe constants of the system, the rate of atomization of the liquid fromthe discharge member 74 may be controlled by the adjustment of the knob96 of the common variable speed transmission 46 to increase the speed ofthe roller 28 for higher rates r 56 shown in Fig. 1.

of atomization and to decrease roller speed when lower rates ofatomization are desired.

In considering the operation of the apparatus described, the atomizer isset into operation by energizing the motor 44, adjusting the knobs 92,94 and 96 of the variable speed transmissions 46, 48 and 94respectively, and energizing the high-voltage source 18 to establish afield of high gradient adjacent to the discharge member 74.

Under these conditions liquid is continually applied to the surface 29in the form of a film the thickness of which is determined either by therate of rotation of the roller 28 and the density, viscosity and surfacetension of the liquid used or by the adjustment of the doctor blade 34when present. However, electrostatic atomization does not take placefrom this liquid film so long as the discharge member 74 is held out ofcontact with the liquid on the surface 29. During periods ofnon-atomization the liquid on the surface 29 moves past the dischargemember and will adhere to the surface due to surface tension until it isreturned to the tank 26. This non-atomizing position of the dischargemember 74 is maintained while switch 90 is open and solenoids and 82 arede-energized. When the sheet 10 engages the lever 91, the switch isclosed, the solenoids 80 and 82 are energized and the discharge member74 is moved into the path of the liquid on the surface 29 which causesthe liquid, when it comes in contact with the discharge member, to bedeformed and transferred to the surface of the discharge member. Theelectrostatic field adjacent the deformed liquid forms it into cuspsfrom the tips of which liquid is electrostatically atomized into a sprayof dispersed particles which are urged toward and deposited on the sheet10. The position of lever 91 of the switch 90 relative to the path ofarticle movement may be arranged so that the discharge member 74 isbrought into atomizing position with the liquid on the surface 29 insuflicient time to apply a coating to the entire exposed surface of thesheet 10 being moved past the discharge member 74.

Because of the shielding effect of the roller, the initial direction ofthe atomized spray will be substantially radial of the roller and thischaracteristic may be utilized to control the direction of the spray inspace. For example, when the discharge member 74 and roller 28 arepositioned as shown in Fig. l the atomized spray moves from thedischarge member 74 generally in a horizontal direction. If the positionof the discharge member 74 is moved concentrically in a clockwise or acounterclockwise direction relative to the roller 28 from the positionshown in Fig. l, the direction of the spray of atomized material ischanged correspondingly in an upward or downward direction.

Fig. 2 shows an atomizing device modified from that shown in Fig. 1 topermit adjustment of the direction of the spray of atomized material.The device is similar to that shown in Fig. 1 except for the mounting ofthe discharge member. As illustrated in Fig. 2, this device includesroller 228, provided with film-supporting surface 229 and shaft 230,which is rotatably mounted on the bearings 232. The roller 228 may berotated by suitable driving mechanism connected to a belt 256, forexample mechanism such as that associated with the belt Liquid may beapplied to the roller 228 by apparatus shown in Fig. l or any othersuitable apparatus. A doctor blade 234 is provided for controlling thethickness of the liquid film on the surface 229. Discharge member 274 issupported on the adjustable brackets 233 by means of supports 278. Thebrackets 233 are adjustably mounted on the bearing structures 232. Theposition of the adjustable brackets may be changed by rotating themrelative to the bearing structures and they may be fixed in any desiredposition by tightening the adjusting screws 235.

In operation this apparatus is similar to the apparatus shown in Fig. 1.However, as mentioned in the description, it has the additional featureof permitting adjustment for changing the direction of the spray ofatomized material issuing from the discharge member 274. This adjustmentmay be carried out by properly orienting the discharge member 274relative to the roller 223 and then fixing this adjustment by tighteningscrew 235.

Fig. 3 shows a further modification of the apparatus shown in Fig. 1. Inthis figure there is shown a sheet Ilitl which is moved in the directionof the arrow 312 by a suitable belt-conveyor 313 past and in spacedrelation to an atomizing apparatus 314. The atomizer comprises a tank325, auxiliary roller 327, feed roller 328, discharge member 374 and ahigh-voltage source 318. In this modification the discharge member 374%is shown as a thin strip and is mounted adjacent to the roller 32' bymeans not shown. The discharge member is connected to the high-voltagesource 318 by means of conductor The tank 326, the rollers 327 and 328and. the discharge member 37 2- are arranged so that liquid from thetank 326 is applied to the auxiliary roller 32.? in the form of a thinfilm as it moves therethrough and upon moving past the feed roller 32%transfers this film to it. As the roller moves past the discharge member374 the liquid film on the roller 32% is transferred to the dischargemember and fio'ws by gravity to the edge 373 remote from the roller 328.The electrostatic field adiacent the edge 373 forms the liquid film intoa series of cusps 3'75 from the tips of which liquid is atomized in theform of a spray and urged downwardly and deposited on the article 35.0.Where it is desired, the rollers 327 and 328 may be covered by housingas shown to reduce to a minimum evaporation of the liquid material as itis being transferred to the discharge member. While a doctor blade isnot sh wn in this embodiment of atomizing apparatus for controlling thethickness of the liquid film prior to its presentation to an atomizingfield it is understood that one could be used in association with theroller 328.

The operation of the apparatus just described is similar to that of theapparatus shown in Fig. 1, the only difference being that the liquid istransferred from the dip tank to the discharge member by passing it overan auxiliary roller in addition to the feed roller.

The apparatus shown in Figs. 4 and 5 permits directing a spray ofatomized material in a vertical plane. In this a paratus a series ofarticles 410 mounted on supports 411 are moved by suitable conveyingmeans indicated by line past and in spaced relation to an atomizer 414.As the articles move past the atomizer 41 a spray of electrostaticallyatomized liquid from the atomizer 414 is deposited on the articles.

'lo effect electrostatic atomization and electrostatic deposition on thearticles 41b, an appropriate potential difference is maintained betweenthe articles 41% and the atomizer This is accomplished by means ofhighvoltage source which may have its ungrounded terminal connected tothe atomizer 414 insulated from ground and its other terminal connectedto the article through ground.

The atomizer 4114 includes an insulating supporting structure ll. onwhich roller 428 is rotatably mounted. The roller 42 3, which is shownas electrically insulating material, is adapted to be rotated about itsaxis by a belt of insulating material which may be connected to anysuitable driving means (not shown). Liquid coating material is appliedto the peripheral surface 429 or" the roller 42% by means of pipe s25made of insulating material whose feed orifice 427 is located adjacentthe upper edge portion of the surface 429.

The liquid may be forced through the pipe '425 by a pressurized fluidsystem similar to the motor, variable speed transmission and pumpcombination shown in Fig.

l or any other suitable system. The liquid flows downwardly along acavity 433 formed along the surface 429 between seal 439 and doctorblade 434 both of which are mounted on bracket 435 which in turn ismounted on the supporting structure H9. The material which does notadhere to the surface 429 as it passes through the cavity 433 isdeposited in receptacle 431 which is formed as a part of the supportingstructure 419. The excess liquid may be returned through pipe 437provided at the bottom of the receptacle 431 to the fluid systemincluding the pipe 425 for further use. Preferably, the supportingstructure 419 includes, in addition to the receptacle 431, ashroud-forming portion which extends upwardly and partially surroundsthe roller 4-28. Such shroud serves, like the shield 40 and housing 34%,to retard evaporation from the exposed liquid film and also to collectand direct into the receptacle 431 any of the liquid which might bethrown from the surface of the roller. As in the apparatus previouslydescribed the doctor blade 434 serves to determine the thickness of theliquid film that is presented for atomization.

A discharge member 474 is supported adjacent the roller 428 and inopposed spaced relation to the articles 416. One end of the dischargemember 474 is supported by fastening means 481 provided at the upperportion of the support structure 415 and its other end is connected tothe tensioning spring 4 51 aflixed to the pipe 437. Intermediate its endthe discharge member 474 passes through guide 477 and over pulley 47?.

Considering the operation of the apparatus just described the articlesllil to be coated are moved past the atomizer 41 by the conveyor 413 andliquid material is applied to the rotating roller at a rate consistentwith its speed of rotation and with the conveyor speed. Under the forceof gravity the liquid spreads over the full longitudinal extent of theperipheral surface of the roller dZ and with the aid of the doctor blade434 the liquid film is maintained at a desirable thickness forpresentation to the discharge member 47%. Upon reaching the dischargemember 4'74 the liquid film is deformed and transferred thereto and thefield of high potential gra dient adjacent the discharge member formsthe deformed liquid into a series of cusps 475 from the tips of whichthe liquid is atomized into a spray, urged toward the articles 4110 anddeposited thereon.

While the apparatus for applying liquid to the feed member is shown as adip tank or a stationary nozzle in the drawings, it is understood thatmy invention is not limited to such showings and may take the form ofany other suitable applicator such as a reciprocating nozzle, etc.

By using a feed roller to present liquid to a site of atomizationasillustrated in the various embodiments shown in the drawings, greateruniformity in the distribution' of the liquid is obtained which isadvantageous in obtaining a more uniform spray pattern. However, theroller required for presenting a uniform, thin film at a site ofatomization necessarily must be of such large diameter that the fieldadjacent the liquid film on its surface is not sufficiently intensewithout deforming the film to electrostatically atomize any liquid fromthe film. By placing a discharge member adjacent the roller so that itwill contact the liquid film on its surface and deform it and also actas a concentrating terminating electrode for lines of force of thefield, I am able to electrostatically atomize liquid in a spray ofimproved uniformity from the surface of such roller.

As shown in Fig. 1, the liquid is deformed by a discharge member whichis in the form of a wire. As shown in Fig. 3 the liquid is deformed by athin strip. However, it is understood that my invention is not limitedto these types of discharge members, as other types of discharge memberswill also operate satisfactorily.

While in each embodiment of my invention illustrated in the drawings thedischarge member is shown in contact with the feed roller, it isunderstood that my invention is not limited to this relationship. Theatomizer will operate satisfactorily with the discharge member spacedfrom the roller so long as it is in contact with the liquid film on itssurface. Of course, it is evident that less liquid is transferred to thedischarge member as the discharge member is moved farther from thesurface of the feed roller and as a result the rate of atomization perunit length of the discharge member is reduced.

Where the liquid has good insulating properties, the discharge membershould be of conducting material. However, most liquids and especiallymost coating materials are sufiiciently conductive that if the dischargemember is made of insulating material the potential can be applied tothe liquid through the film itself.

The feed roller may be either of electrically insulating or conductingmaterial. However, fields of greater intensity adiacent the dischargemember are obtained if the feed roller is of insulating material.

To avoid any sparking between the discharge member and the feed memberwhere the discharge member is mounted so that it may be moved radiallyof the feed member into and out of engagement with it, as illustrated inFig. 1, both the feed member and the discharge member should beconnected to the ungrounded terminal of the voltage source. If only thedischarge member is connected to the ungrounded terminal of the voltagesource, then it is desirable that a suitable switch be provided in thecircuit including the high-voltage source which is adapted to becontrolled by the switch fit) in such amanner that the voltage isapplied to the discharge member only when the discharge member is incontact with the feed member.

The degree of conductivity of the liquid material likewise determineshow great the electrical losses will be along the liquid supply line. Ifthe liquid material has high conducting properties the entire liquidsupply system must be insulated. If, however, liquid material has goodinsulating properties, it may only be necessary to insulate the atomizeritself.

While the present invention is, of course, not restricted to anyparticular design, satisfactory results may be obtained by usingsubstantially the same apparatus described hereinabove and illustratedin Fig. 1, constructed in accordance with the following conditions:

Discharge member 74 Steel wire .01 in diameter. Potential of dischargemember 100,000 volts (negative).

Spacing between discharge member 74 and sheet 10 8 Feed roller 28Balrelite material 6" in diameter and 18 long.

Liquid coating material Synthetic enamel, modified urea formaldehyde 20secs. vis cosity on Zahn #2 Cup,

75 F. Article being coated Sheet steel 18" wide.

The invention can be practiced without regard to the polarity maintainedon the discharge member and the article being coated. In coating, eitherthe discharge member or the article can be grounded or both may bemaintained at a potential different from ground; but, in most instances,it will be more convenient to ground the article. However, anyarrangement which results in maintaining a potential diiference betweenthe article and the coating material and which attracts the coatingmaterial to the article will be satisfactory.

Articles of an insulating character as well as a conducting charactercan be coated with my atomizer. In many instances articles of insulatingcharacter can be coated without the necessity for a backing electrode solong as the surfaces are maintained at a different potential from theatomized material.

This application is a continuation-in-part of my prior application S. N.163,203, filed May 20, 1950, and which is now abandoned.

What I claim is:

1. The method of electrostatically atomizing liquid,

comprising the steps of forming liquid material into a thin, uniformfilm, moving said film into an atomizing zone remote from the site offilm formation, establishing an electrostatic field over said film inthe atomizing zone, and mechanically obstructing movement of said filmin the atomizing Zone along a line transverse to the direction of filmmovement to deform said film locally and thereby increase the gradientof the field at the site of deformation for forming the deformed liquidinto a series of cusps and electrostatically atomizing liquid from thetips of such cusps.

2. The method of electrostatically coating articles, comprising movingarticles over a predetermined path through a coating zone, formingliquid coating material into a thin, uniform film, moving said film fromthe site of film formation to the coating zone in spaced relation to thearticles passing over said predetermined path, establishing anelectrostatic field in the coating zone between said film and thearticles moving over said predetermined path, and mechanicallyobstructing movement of said film in the coating zone to deform saidfilm and thereby increase the gradient of the field locally at the siteof deformation for forming the deformed liquid into a series of cusps,electrostatically atomizing liquid from the tips of such cusps, andelectrostatically depositing the atomized particles on the articles.

3. In electrostatic coating apparatus, a support for an article to becoated, an elongated stationary discharge member having a dischargesurface presented toward and in spaced relation to the supportedarticle, a movable feed member having a liquid film-supporting surfaceadjacent the discharge member remote from the discharge surface, meansfor applying liquid to said liquid film-supporting surface to form afree-surface film thereon, means for driving said feed member for movingthe liquid film thereon into contact with said discharge member andmeans for creating between the supported article and said dischargemember a potential difference sufficiently great to atomize coatingmaterial from said discharge surface and deposit it on the supportedarticle.

4. In electrostatic coating apparatus, means for moving an article overa predetermined path, a discharge member presented in spaced relation tothe article path, a liquid supply means including a feed member fortransferring liquid to said discharge member, means supporting said twomembers for relative movement into and out of liquid-transferringrelationship, means operating in coordination with article movement forbringing said feed member and said discharge member intoliquid-transferring relationship, and means including a high-voltagesource for establishing an electrostatic field between said article andthe coating material on said discharge member for electrostaticallyatomizing and depositing the coating material on the article.

5. Apparatus for applying a liquid coating to an article, a support forthe article, a movable film-supporting member spaced from the supportedarticle, means for applying liquid in the form of a film on saidfilm-supporting member, a film-deforming member located in apredetermined position adjacent said movable member on the side nearestthe supported article and close enough to the movable member to engageand deform the liquid film thereon, and means for maintaining asufficient potential difference between a supported article and thedeformed liquid film to electrostatically atomize liquid from said filmand electrostatically deposit the atomized material on the supportedarticle.

6. In an electrostatic atomizer, a feed member having an extendedsurface for supporting liquid in the form of a film, an extendeddischarge member positioned to engage such film at a transfer zone,means for supplying liquid to the feed member, means for moving one ofsaid members relative to the other in a direction normal to the extentof the discharge member to cause said discharge member to pass throughthe film to create a localized deformation of said film, and means forcreating at the site of such deformation an electrostatic field capableof atomizing fine particles ofliquid from the deformed film.

7. In an electrostatic atomizer, a rotatable feed member having acylindrical liquid-supporting surface, a finewire discharge memberextending parallel and close to said surface to engage liquid thereon,means for applying liquid on the cylindrical surface of the feed member,means for rotating said feed member to cause transference of the liquidthereon to the discharge member, and means for establishing adjacent theliquid on the discharge member an electrostatic field forelectrostatically atomizing the liquid transferred to the dischargemember.

8. In an electrostatic atomizer, a movable feed member having aliquid-supporting exterior surface, means for supplying liquid to theliquid-supporting surface of the feed member, a stationary dischargemember positioned to engage liquid on said surface, means for drivingsaid feed member for moving its liquid-supporting surface past saiddischarge member to transfer liquid thereto, and means for establishingadjacent the liquid on the discharge member an electrostatic field forelectrostatically atomizing the liquid transferred to the dischargemember.

9. The invention set forth in claim 3 with the addition that each ofsaid members possesses a surface presented toward an article on saidsupport, the surface of the feed member having many times the area ofthe surface of the discharge member.

10. in a method of creating a spray of finely divided electricallycharged liquid particles, the steps of distributing liquid over anextended surface, moving the distributed liquid longitudinally of onedimension of said extended surface to an atomizing zone, and at saidzone transferring said liquid from said extended surface onto adischarge member positioned at the atomizing zone said transfer beingalong a line generally transverse of the direction of liquid movementfor atomization from said atomizing zone, and maintaining at suchatomizing zone a particle-charging, atomization-affecting electrostaticfield.

11. In a method of creating a spray of finely divided electricallycharged liquid particles, the steps of distributing liquid over anextended surface, moving the distributed liquid longitudinally of onedimension of said extended surface to an atomizing zone extendingtransverse to the direction of liquid movement, maintaining at suchatomizing zone over the liquid thereat, a particle-charging,atomization-aifecting electrostatic field, and obstructing the movementof the liquid in the atomizing zone along its extent to deform theliquid locally and thereby increase the gradient of the field at thesite of deformation.

12. In an electrostatic atomizer, an extended discharge member having acurved discharge side and a liquid receiving side, a feed member havinga curved liquid-supporting surface, said discharge member being disposedto engage liquid on the surface of the feed member, means for applyingliquid to the surface of the feed member, means for producing at thepoint of closest approach of said members relative movement between themin a direction normal to the extent of the discharge member to causeliquid to be scraped from the feed member onto the discharge member, andmeans for establishing adjacent the discharge side of the dischargemember an electrostatic field for electrostatically atomizing liquid,the radius of curvature of said discharge member at its discharge sidebeing substantially less than that of the liquidsupporting surface ofthe feed member.

13. Means for electrostatically coating articles with a spray ofatomized coating-material particles, a feed member having an extendedexterior surface for supporting a film liquid thereon, means fordistributing liquid as a film over said extended surface, a dischargemember positioned in a transfer zone adjacent said feed member forengaging the liquid thereon, means for causing relative movement betweensaid members at the point where said discharge member engages the liquidfor causing liquid on said feed member to engage said discharge memberand by said engagement to transfer said liquid onto said dischargemember for atomization therefrom in the form of a spray, means forconveying articles in spaced relation and over a predetermined paththrough said spray, and means for maintaining an electrostatic fieldbetween said discharge member and articles so moved through such field,the distance between the articles moving over said predetermined pathand the discharge member being great enough to permit the atomizedparticles of the spray to be dispersed over a substantial area.

14. Means for electrostatically coating articles, comprising a feedmember having an extended surface for supporting liquid in the form of afilm, a discharge member positioned to engage such film at a transferzone, means for supplying liquid to the feed member, means for movingone of said members relative to the other at the transfer zone to causeengagement of the discharge member with the liquid film on the feedmember and by said engagement to transfer liquid to said dischargemember, means for conveying articles over a predetermined path inopposed spaced relation to such zone, and means for creating between thedischarge member and articles moving past the transfer zone anelectrostatic field capable of atomizing liquid at the transfer zoneinto finely divided particles and electrostatically depositing suchparticles on the articles.

15. The invention set forth in claim 6 with the addition that said feedmember is a rotatable roller having a cylindrical film-supportingsurface, means for rotating said roller, and a shroud surrounding saidroller, said shroud being interrupted adjacent said discharge member topermit projection of the atomized particles as a spray.

16. In electrostatic coating apparatus having a support for an articleto be coated and an atomizer for creating a spray of coating-materialparticles to be deposited on the article by an electrostatic field, saidatomizer including a rotating member adapted to support a film of liquidcoating material, means for rotating said member to move the filmcarried thereby to an atomizing zone, a mechanical support for the filmat said atomizing zone, said support providing an edge of small radiusto cause. the film to present an edge of small radius toward an articlefrom which film edge atomization is to take place, means for creating anelectrostatic charge differential between the atomized coating materialparticles and an article, means for supporting an article to be coatedin spaced relation to said rotating member, a shroud enclosing saidrotating member, said shroud being interrupted opposite said supportingmeans to permit the passage of atomized coating material forelectrostatic deposition on the article by said field, a fluid supplysystem for supplying liquid coating material to said rotating member,and means for returning to said supply system any liquid coatingmaterial deposited on the inner surface of said shroud.

17. Apparatus for electrostatically coating articles, comprising aconveyor for moving the articles in succession over a predeterminedpath, an atomizer disposed at one side of said path in spaced relationthereto, said atomizer including a rotatable member adapted to support afilm of liquid coating material, means for rotating said member to movethe film carried thereby to an atomizing zone, mechanical means at saidatomizing zone to form in the film an extended edge portion of smallradius, a coating-material supply system for supplying liquid coatingmaterial to said member for formation into a film thereon, means forcreating an electrostatic field between said edge portion and saidarticles capable of electrostatically atomizing coating material at saidedge portion into a spray of finely divided particles, and meansincluding a shroud partially surrounding said rotating member forcollecting and returning to said supply system liquid coating materialleaving said rotatable member otherwise than in said spray.

18. In a method of producing a spray of electrically charged liquidparticles, the steps of forming a liquid body into an extendedfree-surfaced film, moving said film along a predetermined path to,through, and beyond an elongated atomizing zone extending transverselyof the direction of film movement, maintaining an electrostatic fieldover the surface of said film at the atomizing zone, and mechanicallycontacting the film to increase the curvature of the free surface of thefilm at said atomizing zone to concentrate said field at the area ofincreased curvature.

19. In an apparatus for applying material to the surface of an article,a support for the article to be coated, an extended discharge memberpositioned in spaced relation to the article on said support, means forsupplying liquid coating material to that portion of said dischargemember which faces the article, said means including a surface shieldingmember adjacent and extending along said discharge member on that sidethereof which is remote from the article, means for creating relativemovement between said shielding member and said discharge member in adirection transverse to that in which said discharge member extends, andhigh-voltage means to establish adjacent the material on said dischargemember a potential gradient to transfer said material from saiddischarge member to said article surface, said motion producing meansbeing power driven and operative during the material transfer operation.

7 References Cited in the file of this patent UNITED STATES PATENTS

1. THE METHOD OF ELECTROSTATICALLY ATOMIZING LIQUID, COMPRISING THESTEPS OF FORMING LIQUID MATERIAL INTO A THIN, UNIFORM FIL, MOVING SAIDFILM INTO AN ATOMIZING ZONE REMOTE FROM THE SITE OF FILM FORMATION,ESTABLISHING AN ELECTROSTATIC FIELD OVER SAID FILM IN THE ATOMIZINGZONE, AND MECHANICALLY OBSTRUCTING MOVEMENT OF SAID FILM IN THEATOMIZING ZONE ALONG A LINE TRANSVERSE TO THE DIRECTION OF FILM MOVEMENTTO DEFORM SAID FILM LOCALLY AND THEREBY INCREASE THE GRADIENT OF THEFIELD AT THE SITE OF DEFORMATION FOR FORMING THE DEFORMED LIQUID INTO ASERIES OF CUSPS AND ELECTROSTATICALLY ATOMIZING LIQUID FROM THE TIPS OFSUCH CUSPS.